Electrical stimulation of the posterior spinal cord, spinal cord stimulation (SCS), has developed into an effective therapeutic tool for treating chronic pain conditions. However, very little is known about the sites of activation or the neural mechanisms evoked by SCS that relieve pain and promote changes in the function of somatic and visceral structures.
Spinal Cord Stimulation is most commonly used for patients with chronic intractable pain syndromes. It has also been useful for treating movement disorders and is occasionally used following head injuries. However, one complication with SCS is that of accommodation or habituation to the stimulation signal. Companies that manufacture spinal stimulation devices have developed complex stimulation programs and devoted chapters on techniques to reduce the problem of accommodation during SCS (Alfano S, Darwin J, Picullel B: Spinal Cord Stimulation, Patient Management Guidelines for Clinicians, Medtronic, Inc.). Accommodation is when the body habituates or becomes accustomed to an activity or signal and then starts to ignore or ‘tune it out’. By varying the signal or keeping the focal point of the signal moving, accommodation can be minimized.
Dorsal Column Stimulation (DCS) or SCS using an electrical current pattern has shown to be a cost benefit in treating chronic pain disorders in patients (Dorsal column stimulation: cost to benefit analysis; Acta Neurochir Suppl (Wien), 52( ): 121-3, 1991).
SCS stimulates the dorsal column in a somewhat superficial manner as pointed out by Holsheimer (Holsheimer J: Which Neuronal Elements are activated Directly by Spinal Cord Stimulation, Neuromodulation, Volume 5, Number 1: 25-31, 2002). The electrodes are normally attached to the dura matter in the epidural space, and most of the current distribution remains in the cerebrospinal fluid (CSF) and does not project deeply into the dorsal column.
Thus, traditional SCS stimulation has limited application because of the spread of the stimulating electrical field within the CSF as intensity of stimulation increases. This is due to the highly conductive nature of the CSF as compared to the less conductive nature of the spinal cord tissue itself. Thus, traditional SCS stimulation is “amplitude limited” to a relatively narrow surface area of the spinal cord. Frequently, patient satisfaction with electrical stimulation is compromised by the recruitment of adjacent neuronal structures that, when activated, can create discomfort, motor contractions, and outright pain. The efficacy of the therapy is thus limited.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies with regard to accommodation or habituation to the spinal cord stimulation signal when used in the treatment of chronic pain syndromes.